Polymer compositions containing oxygen scavenging compounds

ABSTRACT

An oxygen scavenging composition or concentrate of a carrier, such as a polymer, which is permeable to both oxygen and water or water vapor and an oxygen scavenging compound of an organic compound or salt thereof dispersed relatively uniformly throughout the polymer in an amount effective to act as an oxygen scavenger. The oxygen scavenging compound may be an ascorbate compound or a polycarboxylic or salicylic acid chelate or complex of a transition metal or a salt thereof. The oxygen scavenging composition is activated for scavenging oxygen by contact with water or water vapor which permeates into or through the carrier.

This application is a continuation of application Ser. No. 08/444,611filed May 19, 1995 (abandoned), which is a continuation of applicationSer. No. 07/962,424 filed Oct. 16, 1992 (abandoned) which is aContinuation-In-Part of U.S. Ser. No. 07/518,041 filed May 2, 1990(abandoned) and a Continuation-In-Part of U.S. Ser. No. 07/581,507 filedSep. 12, 1990, now U.S. Pat. No. 5,202,052.

BACKGROUND OF THE INVENTION

The present invention relates to a polymer composition containing oxygenscavenging compounds therein, for use in packaging beverages, foods,pharmaceuticals and the like. In particular, these polymer compositionshave utility as liners or gasketing materials for crowns, closures, lidsor caps of various containers such as bottles or cans to prevent oxygeningress and to scavenge oxygen which is present inside the container, orcontained in outside air leaking past or permeating through the polymercomposition. These polymer compositions may also be used in theconstruction of the container, as the container material itself, as acomponent of a container, or as a barrier layer thereupon or therein, toprevent oxygen ingress therethrough or to scavenge oxygen therein.

In packaging oxygen sensitive materials such as foodstuffs, beverages,and pharamceuticals (collectively “products”) oxygen contamination canbe particularly troublesome. Care is generally taken to minimize theintroduction of oxygen or to reduce the detrimental or undesirableeffects of oxygen on the foodstuff or beverage.

Molecular oxygen (O₂) can be reduced to a variety of intermediatespecies by the addition of one to four electrons; these species aresuperoxide, hydroxy radical, hydrogen peroxide, and water. O₂ and waterare relatively unreactive: the three intermediate species are veryreactive. Also, O₂ can be activated to singlet electron state oxygen(which can undergo subsequent reduction to the more reactive oxygenspecies) by irradiation, or by the presence of catalytic agents. Thesereactive oxygen species are free radical in nature, and the oxidativereactions in which they participate are therefore autocatalytic.

Carbon-carbon double bonds are particularly susceptible to reaction withthe intermediate species. Such carbon-carbon bonds are often found infoods and beverages, pharmaceuticals, dyes, photochemicals, adhesives,and polymer precursors. Virtually any product which has complex organicconstituents will contain such carbon-carbon double bonds or otheroxygen reactive components, and hence can undergo oxidative reactions.Thus, if the oxidation products adversely affect the performance, odoror flavor of the product, then removing the oxygen which is present(either dissolved in or trapped with the product), preventing oxygeningress, or inhibiting the reactions of oxygen will benefit the product.

A number of strategies exist to deal with oxygen as a contaminant. Themost basic is simply to remove oxygen from the product by vacuum or byinert gas sparging, or both. Such systems are used in boiler watertreatment, the orange juice and brewing industries, and inmodified-atmosphere packaging of food products. This technology, whilesomewhat equipment intensive, can remove about 90-95% of the oxygenpresent in air from the product (or its container) prior to or duringpackaging. However, the removal of the remaining 5-10% of oxygen usingthis approach requires longer times for vacuum treatment and/or spargingand increasingly larger volumes of higher and higher purity inert gaswhich must not itself be contaminated with trace levels of oxygen. Thismakes the removal (by such methods) of the last traces of oxygenexpensive. A further disadvantage of these methods is a tendency toremove volatile product components. This is a particular problem withfoods and beverages, wherein such components are often responsible forsome or all of the aroma and flavor.

Herein, the term “oxygen scavenger’ means materials or chemicalcompounds which can:

a) remove oxygen from the interior of a closed package by reacting orcombining with entrapped oxygen or with oxygen that is leaking into thepackage interior past the package/closure sealant or gasket;

b) prevent or reduce the perfusion of oxygen through thegasketing/sealant materials between container and closure;

c) prevent or reduce the perfusion of oxygen through the materials ofthe package/closure itself by incorporation of the oxygen scavenger intothe materials of which the container/closure is/are made;

d) prevent or reduce the perfusion of oxygen through the material of thepackage/closure itself by incorporation of the oxygen scavenger into oneor more layers of a multilayer container/closure construction.

The term “antioxidants” as used herein means materials or compoundswhich, when added to the foodstuff or beverage itself, slow the rate ofoxidation or otherwise reduce the undesirable effects of oxidation uponthe foodstuff or beverage.

For example, it has been known since the 1930's that oxygen in beeradversely affects its flavor and stability. Amounts of oxygen as low as0.1 to 0.2 ml per 355 ml container will, over time, cause darkening ofthe beer, an increase in chill-haze values and significant tastechanges. Oxygen's effect on beer is so strongly detrimental that manybrewers go to great lengths to remove it from the bottle during thefilling process. One usual technique is to (1) remove the air (viavacuum) from a clean bottle; (2) fill the bottle with CO₂; (3) flow thebeer down the bottle wall into the bottle thus displacing the CO₂; and(4) finally, to squirt a jet of high-pressure deoxygenated water intothe bottle to cause the beer to over-foam just as the cap is put on(attempting thereby to displace the remaining headspace gases with thebeer's own CO₂). In addition, to minimize introduction of air (21% O₂)into the headspace just before capping, production lines are run moreslowly than otherwise necessary. All this is expensive, and usuallyreduces the total O₂ concentration in the headspace to only about200-400 parts per billion: the desired level is as close to zero aspossible, but certainly below about 50 ppb. The 200-400 ppb achieved inthe packaged product by careful brewers corresponds to approximately50-100 microliters of oxygen per 355 ml bottle. Even this small quantityof oxygen is still considered to be one of the major limitations onquality and shelf life of beer today.

Many other food products suffer similar oxygen-mediated degradation; forexample, individual portions of prepared foods are marketed incontainers made of plastics, and air entrapped therein, and leaking orperfusing into the package after processing, is an acknowledged industryproblem. This leakage or perfusion is often especially true for packagesmade entirely of plastics, because many plastics with otherwisedesirable properties are relatively permeable to oxygen. Incorporationof the present invention into the bulk of such plastics, or into one ormore layers of a multilayer package, could be beneficial in reducing oreliminating such perfusion. Among obvious benefits of such applicationsof the invention is extended shelf life.

None of the above techniques remove or control (a) oxygen dissolved inthe product (which will outgas into the headspace as the enclosed systemcomes to equilibrium), or (b) oxygen leakage into the package past thegasket/container interface, or (c) oxygen permeating through the gasketinto the interior of the package, or (d) oxygen permeating through thecontainer itself into the package. The present invention also aids inremoval of O₂ from these other three sources. Furthermore, it is knownthat free oxygen inside a package may yield very rapid degradation ofthe product, consequently a desired property of any scavenger is toremove most of the free oxygen as quickly as possible (i.e., ultimate O₂absorption capability is subordinate to fast uptake kinetics).

Antioxidants (such as sulfur dioxide, trihydroxy butyrophenone,butylated hydroxy toluene and butylated hydroxy anisole) and oxygenscavengers (such as ascorbic acid, isoascorbic acid and glucoseoxidase-catalase) have been used in an attempt to reduce the effects ofoxygen contamination on beer (See e.g., Reinke et al., “Effect ofAntioxidants and Oxygen Scavengers on the Shelf-life of Canned Beer,”A.S.B.C. Proceedings, 1963, pp. 175-180, Thomson, “Practical Control ofAir in Beer”, Brewer's Guild Journal, Vol. 38, No. 451, May 1952, pp.167-184, and von Hodenberg, “Removal of Oxygen from Brewing Liquor,”Brauwelt International, III, 1988, pp. 243-4). The direct addition ofsuch agents into beer has several disadvantages. Both sulfur dioxide andascorbates, when added to beer, can result in production of off-flavorsthus negating the intended purpose of the addition. Many studies havebeen conducted on the effect of such agents on the flavor of beer. (Seee.g., Klimowitz et al., “The impact of Various Antioxidants on FlavorStability,” MBAA Technical Quarterly, Vol. 26, pp. 70-74, 1989 and Grayet al., “Systematic Study of the Influence of Oxidation on Beer Flavor,”A.S.B.C. Proceedings, 1948, pp. 101-112.) Also, direct addition of suchcompounds to a food or beverage requires stating on the label that theproduct contains the additive. This is somewhat undesirable in today'sera of “fresh” and “all-natural” products.

It is also known in the art to prepare plastic containers (e.g., forbeer, other beverages and various foods) wherein a wall comprises, orincludes a layer which comprises, a polymer, an oxidizable componenthaving oxygen-scavenging properties, and a metal catalyst, for bindingany oxygen penetrating the container wall (see, e.g., Folland, the OXBARSuper-Barrier System: A Total Oxygen Barrier System for PET Packaging,“EUROPAK '89, Oct. 30-Nov. 1, 1989, and European Patent Application301,719). Also, U.S. Pat. No. 4,048,361 discloses a food containerhaving at least one barrier layer which contains an oxygen “getter,”while U.S. Pat. No. 3,586,514 discloses a thin wall polyvinyl chloridecontainer wherein the plastic contains a quantity of an antioxidizingagent to reduce oxygen permeability therethrough, and Japanese patentapplication 58-160,344 discloses hollow moldings of a polyethyleneterephthalate (“PET”) with a meta-xylene group containing polyamideresin. The containers described in these references are described asoxygen barriers which prevent or reduce the transmission of oxygenthrough the wall and into the container. Such products are generallymore expensive than glass containers and are less likely to be recycledthan glass or aluminum containers.

Attempts have been made to incorporate oxygen scavenging systems in acontainer crown or closure. For example, U.S. Pat. No. 4,279,350discloses a closure liner which incorporates a catalyst disposed betweenan oxygen permeable barrier and a water absorbent backing layer. Anotherclosure is disclosed in UK Patent Application 2,040,889. This closure isin the form of a stopper molded from ethylene vinyl acetate (“EVA”)having a closed-cell foamed core (which may contain water and sulfurdioxide to act as an oxygen scavenger) and a liquid impervious skin.Also, European Patent Application 328,336 discloses a preformedcontainer closure element, such as a cap, removable panel or liner,formed of a polymeric matrix containing an oxygen scavenger therein.Preferred scavengers include ascorbates or isoascorbates, and theirscavenging properties are activated by pasteurizing or sterilizing theelement after it has been fitted onto a filled container. Similarly,European Patent Application 328,337 discloses a sealing composition fora container closure comprising a polymeric matrix material which ismodified by the inclusion therein of an oxygen scavenger. Thesecompositions may be in fluid or meltable form for application to aclosure or to be present as a deposit on the closure in the form of aclosure gasket. Ascorbates or isoascorbates, alone or in combinationwith sulfites, are preferred oxygen scavengers. Again, the scavengingproperties of these compounds are activated by pasteurizing orsterilizing the deposit when sealing a container with the gasket on aclosure or metal cap.

Ferrous oxide has been used commercially as an oxygen scavenger for foodapplications. It is currently manufactured in sachets or packets by anumber of firms including Mitsubishi Gas Chemical, Inc., which marketsit in a product known as AGELESS™. (See, e.g., European PackagingNewsletter and World Report, Vol. 21, No. 7, July, 1988.) Such productsmay also contain ascorbates as an oxygen scavenging agent, per U.S. Pat.No. 4,752,002. Also, U.S. Pat. No. 4,524,015 discloses the use of agranular mixture of an ascorbate or ascorbic acid, an alkali metalcarbonate, an iron compound, carbon black, and water, and U.S. Pat. No.4,384,972 discloses a foodstuff freshness keeping agent of a particulatecomposition that contains a salt of a metal, an alkali substance, asulfite or other deliquescent compound, and optionally, ascorbic acid ora salt thereof.

While such products are effective at removing oxygen from withinpackages of breads, cookies, pasta, coffee and other relatively dryfoodstuffs, they have significant drawbacks. They (a) are hygroscopicand water soluble to some extent, (b) function less effectively in highCO₂ environments, (e.g., beer containers), (c) in order to preservetheir activity, they must be carefully sequestered from air (or otheroxygen-containing environments) until use, and (d) they require a sachetor packet, often of multilayer construction, for proper storage andhandling of the oxygen scavenger.

U.S. Pat. Nos. 4,536,409 and 4,702,966 each disclose a multilayer wallconstruction for a polymeric container to be used to pack comestibles,wherein outer and inner layers are structural and protective layers:positioned therebetween are materials designed to control the unwantedpermeation of oxygen. Preferably, the outer and inner layers areolefinic and resistant to the transmission of water vapor at roomtemperature, but at elevated temperatures, they permit water vapor topermeate into the oxygen absorbing system to trigger such system to anactive state which is capable of absorbing oxygen. While thisconstruction is useful from the standpoint of retaining the oxygenabsorbing system in a dormant state until it is needed, suchconstruction requires heat to render the inner and outer layerspermeable to water vapor which can trigger or activate the oxygenabsorbing system.

Consequently, there is a need for a material or product which canrapidly reduce oxygen levels inside a package of products which are wetor moist (or which are capable of generating moisture inside theirpackaging) without adversely changing taste, aroma, or functionality ofsuch packaged foodstuffs, beverages and pharmaceuticals. Persons skilledin the art have considered the addition of various agents into thepackaging of such products in an attempt to meet this need.

Japanese patent application 61-238,836 discloses a packaging film madefrom a thermoplastic such as low density polyethylene (“PE”), whichincludes ascorbic acid alone or in combination with an aliphaticpolycarboxylic acid. This film is disclosed as having good gas barrierproperties.

Japanese patent application 54-022,281 discloses a fruit tray made of athermoplastic foam base having a thin layer of ascorbic acid orerythorbic acid (or one of their alkali metal salts) on the face ofindentations in the tray upon which the fruit is to be placed.

New oxygen absorbing and scavenging materials are also being developedby Aquanautics, Inc., Alameda, Calif. (See Packaging Technology, “OxygenEliminator Extends Shelf Life,” 1989 and “Extending the Life of a Bottleof Beer,” New York Times, Mar. 29, 1989). These materials are transitionmetal complexes, particularly (but not exclusively) those complexesformed between transition metals and “polyalkylamines” (as disclosed inU.S. Pat. No. 4,959,135, which is expressly incorporated herein byreference thereto), as well as those complexes formed between transitionmetals and “macrocyclic amines” (as disclosed in U.S. Pat. No.4,952,289, which is expressly incorporated herein by reference thereto).

These “amine+metal” complexes can bind ligands such as oxygen and can beused as oxygen scavengers in packaging. The complexes either do not formor do not become activated (i.e., cannot, or do not, bind oxygen) untilthe amine and metal are together exposed to water or water vapor. Theingredients of the complex can be mixed and used either free, orimmobilized on or within a support inter alia, on or mixed with siliconerubber or with a polymer such as polyvinyl chloride (“PVC”), EVA,polypropylene (“PP”), PE or polyurethane (see e.g., U.S. patentapplication Ser. No. 07/317,172, filed Feb. 28, 1989, the content ofwhich is expressly incorporated herein by reference thereto, wherein oneuse for such complexes is as an oxygen scavenger in sealing compositionsand structures for beer bottle crowns).

Salicylic acid complexes and their reactivities towards oxygen aregenerally known and are described in Zanello et al., Inorganica Chim.Acta 1983, Vol. 74, pp. 89-95 and Cini et al., Inorganica Chim. Acta1984, Vol. 88, pp. 105-113.

U.S. Pat. No. 4,287,995 discloses a sealing member for a container whichis used to preserve aqueous liquids therein. This sealing member ismounted on the cap or stopper of the container on the portion facing thecontents. The sealing member contains an oxygen absorbent which isseparated from contacting the contents of the container by a film whichhas a plurality of fine openings such that it is gas-permeable butwater-impermeable at one atmosphere pressure.

U.S. Pat. No. 4,510,162 discloses an oxygen absorbent compositioncomprising iron particles, yeast and moisture, which mounted on asuitable carrier and adapted to be mounted in a closable container forremoving oxygen therefrom.

U.S. Pat. No. 4,756,436 discloses a construction for an oxygenscavenging composition to be installed in a cap upon a liquid substancecontaining vessel. This construction includes an upper, vacantcompartment, a lower compartment containing the oxygen scavenger, and apartition therebetween. The partition is made of single or plural sheetsof gas permeable liquid-proof material to provide a barrier between theoxygen scavenger and the liquid substance.

Current crown liner technology includes the in situ molding of athermoplastic liner material directly in the crown which will later beused for bottling beer or other beverages. Such liners are primarilymade of PVC in the United States and of thermoplastics which do notcontain chlorine (such as EVA or PE) in Europe and Japan.

PVC compositions, with or without additives as stabilizers or forimparting certain properties, are known in the art. For example, U.S.Pat. No. 4,380,597 discloses a stabilized thermoplastic composition ofPVC (or mixed polymers) which may include ascorbates or gluconates asstabilizer additives. These stabilizers are added not to absorb oxygenfrom inside packages made of the polymer, but to prevent breakdown ofthe polymer itself. U.S. Pat. No. 4,211,681 discloses shaped articles(e.g., films or tubes) which include high molecular weight poly(ethylene oxide) polymers with stabilizers of ascorbic acid, 2,3-butylhydroxyanisoles, and the like.

Japanese patent application 62-215,010 discloses a deodorizing fiberobtained by treating thermoplastic fibers with inorganic particles ofdivalent ferrous iron and L-ascorbic acid. U.S. Pat. No. 4,278,718discloses a sealing composition for beverage containers consistingessentially of a vinyl chloride resin, a plasticizer, and a metal oxide.

Today there is a need for oxygen-scavenging thermoplastic compositionsfor use in oxygen-scavenging systems for packaging beverages, foods,pharmaceuticals and other products. The oxygen-scavengers in suchsystems should rapidly reduce oxygen levels within the package (and/orin the goods themselves), as well as prevent oxygen ingress into thepackage. There is a particular need for such systems where the internalenvironment of the package is (or can become) wet or moist. Mostadvantageously, the oxygen-scavengers of such systems would remaininactive until after the product is packaged. One particular need forsuch a composition is a liner for beer bottle crowns wherein theoxygen-scavenging properties of the liner do not become active untilafter the bottle is crowned.

Other particular uses of such a composition may involve dry productspackaged under low relative humidity. In such cases, the compositions ofthis invention may be activated by application of water or water vaporto the composition itself immediately prior to sealing of the container.For example, in the case of a dry product to be sealed in a container bymeans of a screw-on lid with a gasket comprising a composition of thisinvention, activation moisture might be provided by a water-mist spray,by dipping in water, by exposure of the lid to a water-vapor-saturatedatmosphere, or by incidental exposure to steam during pre-cappingsterilization. The present invention provides certain compositions andformulations as solutions to these general needs, and specifically forbottled beverages including beer.

SUMMARY OF THE INVENTION

This invention teaches the preparation and use of certain oxygenscavenging materials dispersed in various carriers, such as polymers orplastics, and used in packaging as oxygen scavenging compositions. Thesecompositions, by virtue of novel and unexpected increases in oxygenuptake rates of the oxygen scavenging material, are useful in preventingdeterioration or reaction of the packaged substances due to exposure tooxygen in the package.

In one embodiment of the invention, the oxygen scavenging compositioncomprises a carrier, such as a polymer, preferably a thermoplasticpolymer, which is permeable to oxygen and water or water vapor; anorganic compound, added in an amount sufficient to act as an effectiveoxygen scavenger and which is capable of reacting with oxygen beingdispersed relatively uniformly through the carrier; and a catalyzingagent in an amount sufficient to increase the rate of oxygen uptake bythe organic compound in order to provide rapid initial oxygenscavenging.

Preferred organic compounds include D- or L-ascorbic acid or a salt orfatty acid derivative thereof (i.e., D- or L-ascorbates). Isoascorbatesor erythrobates may also be used, but most preferably, the organiccompound is sodium L-ascorbate, since it is readily available and knownto be safe for contact with foodstuffs or beverages.

The catalyzing agents for these ascorbates includes any transitionmetal, compound, complex or chelate. The transition metal is preferablychosen from the group comprising iron, copper, cobalt, or nickel, andmost preferably it is either iron or copper. The transition metal maypreferably be supplied either (1) as a compound such an ordinary salt,or (2) as a polyalkylpolyamine (“PAPA”) chelate, macrocyclic amine(“macrocycle”) chelate, an amino polycarboxylate chelate, or asalicylate chelate of a transition metal ion. It is also possible toinstead utilize other transition metal chelates or complexes whichcontain one or more amine, hydroxyl, carboxylate or sulfhydryl groups,or combinations thereof.

Simple transition metal salts such as ferrous or ferric chloride,cuprous or cupric chloride, ferrous or cupric sulfate, ferrousgluconate, nickel sulfate, or cobalt chloride, are suitable ascatalyzing agents for the ascorbates, and of-these salts, cupric orferric sulfates are preferred. The transition metal chelates areparticularly useful because, when utilized in the appropriate amounts,they possess oxygen scavenging properties which augment the oxygenscavenging properties of the ascorbate compound, thus making thetransition metal chelate a secondary scavenging compound, while thetransition metal ion in the chelate or complex can catalyze the oxygenscavenging activity of the ascorbate compound.

Of the chelated ion complexes, transition metal chelates of ethylenediamine tetracetic acid (“EDTA”) are advantageous, with monoferrousdisodium EDTA [Fe⁺⁺/EDTA/2Na⁺] being the most preferred. Transitionmetal chelates of polyalkylpolyamines are also useful, with those amineshaving symmetrical-length carbon chains between adjacent nitrogen atomsbeing preferred. The most preferable of those amines have symmetriccarbon chains which each comprises between one and four, and optimallytwo, carbon atoms. Transition metal chelates of salicylates orsalicylate salts can also be used in practicing this invention. As notedabove, each of these chelates provides oxygen scavenging activity toaugment that of the ascorbate, while the transition metal ion catalyzesthe ascorbate compound when exposed to moisture.

In another embodiment of the invention, the oxygen scavengingcomposition comprises a transition metal complex or chelate of apolycarboxylic or salicylic acid dispersed relatively uniformly throughthe carrier and added in an amount sufficient to act as an effectiveoxygen scavenger. The polycarboxylic acid is preferably an aminopolycarboxylic acid, and most preferably EDTA. Other usefulpolycarboxylic acids include ethylene diamine triacetic acid,hydroxyethylene diamine triacetic acid, diethylene triamine pentaaceticacid or trans-1,2-diamino cyclohexane tetraacetic acid.

It is also possible to utilize other polycarboxylic acids, such ascitric and oxalic acids, which are capable of forming a chelate with thetransition metal. Such polycarboxylic acids may also contain one or moreamine hydroxyl, carboxylate or sulfhydryl groups, or combinationsthereof. Alternatively, transition metal chelates or complexes ofsalicylic acid or salicylates, whether or not substituted, can also beused instead of the amino polycarboxylic compounds. Salts of any ofthese acids are also suitable.

Again, the transition metal of the chelate is preferably iron, copper,cobalt, or nickel; most preferably it is either iron or copper. Thetransition metal used to make the chelate or complex may be supplied asa simple salt, such as iron or copper chloride, iron or copper sulfate,iron gluconate, nickel sulfate, or cobalt chloride, but is present aspart of the chelate or complex.

It is also possible, and in some cases preferred, to include a reducingagent, such as an ascorbate compound, in the polymer in an amountsufficient to enhance, preserve or augment the oxygen scavengingproperties of the transition metal chelate or complex. The ascorbatereduces the oxidation state of the transition metal ion of the chelateso that the ion can be oxidized when the chelate contacts oxygen. Thisenhances the oxygen scavenging properties of the chelate. Aparticularly, preferred combination illustrates this embodiment of theinvention is monoferric monosodium EDTA [Fe⁺⁺⁺/EDTA/Na⁺] in combinationwith sodium ascorbate as a reducing agent. Ascorbic acid, in its D- orL-form, or a derivative, analog or salt thereof, as described above, maybe used as a preferred reducing agent, since it has oxygen scavengingproperties.

Preferred polymers for use as carriers include polyolefins, PVC,polyurethanes, polyamides and elastomers. PVC, EVA and PE are typicallyutilized, but PET, PP, and other olefins, ethylene/alpha-olefincopolymers, ethyl octene copolymers, various thermoplastic (or other)polyurethanes, elastomers, such as isoprene rubber, nitrile rubber,chloroprene rubber, silicone rubber, or other rubber analogs, and otherthermoplastic materials such as chlorinated polyethylene (“CPE”),SURLY™, or various combinations or mixtures thereof, are acceptable. Inaddition, sprayed or dipped coatings of epoxies, polyesters or otherconventional coating materials are useful as carriers for the oxygenscavenging compositions of the invention.

The most preferred polymers or other materials which may be used as thecarrier are those which are pervious to water vapor at room temperature,so that exposure to elevated temperatures is not necessary to activatethe oxygen scavenging capabilities of the composition. The oxygenscavenging material is uniformly dispersed in and throughout the carrierby a direct mixing technique. Advantageously, the oxygen scavengingmaterial is mixed or blended into the carrier in a dry state. The oxygenscavenging capabilities of these compositions are later activated bycontact with water or water vapor which permeates into or through thecarrier. The water vapor may be provided by the package contents or, fordry contents, may be introduced separately before sealing the package.

Another embodiment of the invention relates to a package (for, e.g., afoodstuff, beverage, or pharmaceutical product) comprising means forsupporting or retaining the product, and an oxygen scavengingcomposition material in contact with the product (or in contact with theenvironment between the product and the package) for scavenging oxygentherefrom so as to avoid detrimental effects to the performance, odor orflavor properties of the product.

The oxygen scavenging composition may be present on an inside surface ofthe product supporting or retaining means. This means can be in the formof a carrier film, with the oxygen scavenging composition beingdispersed relatively uniformly throughout the carrier film. If desired,one or a plurality of polymer films may be used, with at least one layerof adhesive or binder therebetween, with the oxygen scavengingcomposition being present in at least one of the polymer films orlayers. Also, the oxygen scavenging composition can be applied as acoating or lining upon the inside surface of the product supporting orretaining means to function as a barrier to oxygen permeation.

The invention also relates to containers for water-containing foodstuff,beverage, chemical or pharmaceutical products comprising means forretaining the product and having at least one opening therein forfilling or dispensing of the product; a member for closing the openingand preventing escape of the liquid product when not desired; and aliner or gasket comprising one of the oxygen scavenging compositionsdescribed above and being positioned adjacent the closing member.Preferably, the retaining means is a can, jar or bottle, the closingmember is a crown or closure, and the polymer of the liner or gasketcomprises a polyurethane, PVC, EVA or PE. The retaining means may alsobe a metal can or glass jar, with the closing member being a lidtherefore. In this variation, the oxygen scavenging composition may beapplied to the lid in the form of a ring, a spot, or coating. Also, theoxygen scavenging composition may be applied to the interior of the canas a coating, generally of an epoxy or polyester carrier. When a metalcan is used, it is usually provided with a seam. Thus, it is possible toapply the oxygen scavenging compositions of the invention as a sealantin or upon the seam to prevent oxygen ingress into the can through theseam.

Another embodiment of the invention relates to an oxygen scavengingcontainer which may be made from any one of the compositions of theinvention described above. Yet another embodiment relates to amultilayer container or closure where one or more layers comprise theoxygen scavenging compositions of the invention. Also, thesecompositions may be used as a sealant for, or in an article trapped bythe closure methodology for packaging which does not include anidentifiable closure which is differentiable from the material of thecontainer itself.

In another aspect of the invention, an oxygen scavenging concentrate isprovided. The concentrate may contain many of the same ingredientsdescribed above in connection with the oxygen scavenging compositions.For example, in some embodiments, the concentrates include a carrier, anoxygen scavenging material, and a catalyzing agent. The concentratesdepart from the compositions described above by having substantiallyhigher concentrations of active components, i.e. oxygen scavengers andcatalysts. In preferred embodiments, the concentrates of this inventioncontain about 10 to 50% oxygen scavenging material and about 0.3 to 8%catalyzing agent, depending, of course, on the desired use of theconcentrate and the particular components employed. In one specificembodiment, the concentrate includes about 10 to 50% by weight sodiumascorbate and about 0.3 to 8% by weight copper sulfate in a polyethylenecarrier. Of course, other carriers such as ethylene vinyl acetate orpolyvinyl chloride are suitable for many embodiments.

In a further aspect of the invention, a two-part composition and methodfor using such composition is provided. The two-part system includesseparate oxygen scavenger and catalyst concentrates which are combinedto obtain the final reactive composition. In some embodiments,additional base resin is added to dilute the concentrates during thecombination step. Each concentrate includes a carrier that is typicallya resin or other material described in connection with the embodimentsdescribed above. The concentrates also include either an oxygenscavenging material or catalyzing agent (as described above), but notboth. Thus, the oxygen scavenger concentrate includes an oxygenscavenging material dispersed throughout a carrier that is substantiallyfree of catalyst. Likewise, the catalyst concentrate includes a catalystdispersed throughout a carrier that is substantially free of oxygenscavengers. In this context, a composition is “substantially free” of acomponent when that component is present in a sufficiently smallquantity that it has no effect on the desired activity of thecomposition. Thus, for example, an oxygen scavenger concentrate that issubstantially free of catalyst can be extruded and quenched in waterwithout undergoing reactions that consume the oxygen scavenger.

A further understanding of the nature and advantages of the inventionsherein may be realized by reference to the remaining portions of thespecification and the attached drawings.

DETAILED DESCRIPTION OF THE INVENTION

The oxygen scavenging compositions of the invention include certainpreferred combinations of oxygen scavenging and catalyzing agents whichare added to and dispersed in and throughout a carrier for these agents.

The most preferred oxygen scavenging agent of the invention is anascorbate compound which is used in combination with a transition metalchelate of EDTA. The term “ascorbate compound” is used to includeascorbic acid in either its D or L form and any derivative, analog orsalt thereof, including erythorbic acid. In particular, D- or L-ascorbicacid, and their sodium, potassium or calcium salts, or fatty acidderivatives may be used in this invention. Certain of the above,especially the sodium ascorbate salts, are particularly preferred sincethese materials are widely accepted for contact with food and haveachieved “Generally Recognized As Safe” (or “GRAS”) status with the U.S.Food and Drug Administration for such applications.

An advantage in practicing this invention is that the oxygen scavengingcompositions do not become active for scavenging oxygen until theycontact water or water vapor. Thus, the selected composition or compoundis dispersed relatively uniformly throughout a carrier which ispermeable both to oxygen and water or water vapor. Thereafter, when thecarrier is used in an application adjacent to or in the vicinity of awater bearing foodstuff, pharmaceutical, chemical, or beverage, water orwater vapor will permeate into the carrier and thus activate theascorbate compound for removal of oxygen. By retaining the carrier in adry environment prior to use, the oxygen scavenging compound will remainessentially dormant until activated. For dry products, the oxygenscavenging ability of the compound or composition may be activated byexposure to non-product water or water vapor before sealing thecontainer.

The inclusion of a catalyzing agent with the ascorbate compound greatlyenhances the rate of oxygen scavenging after the ascorbate compound isactivated by exposure to water or water vapor. It has been found that atransition metal compound, in the form of an organic or inorganic salt,or as a complex or chelate, is useful in accelerating (i.e., catalyzing)the rate of oxygen scavenging by an ascorbate compound. The preferredcatalysts include the transition metal chelates of EDTA. The mostpreferred catalysts are the iron complexes of EDTA or sodium saltsthereof. Monoferrous disodium EDTA [Fe⁺⁺/EDTA/2Na⁺] and monoferricmonosodium EDTA [Fe⁺⁺⁺/EDTA/Na⁺] are the most preferred chelate. It isalso suitable to use a simple iron or copper salt, such as iron chlorideor sulfate or copper chloride or sulfate. Typically, the carrier ismixed with the ascorbate compound for uniform dispersion throughout thecarrier. Subsequently the catalyst is added to form the desiredcomposition which is activated by contact with water or water vaporwhich permeates the carrier. The combination of an ascorbate andtransition metal compound enables the ascorbate compound to be oxidizedrapidly at low pH values (e.g., at pH values between 4 and 5) which aretypically encountered in many foods including bottled beer and manyfruit juices.

In another embodiment of the invention, the oxygen scavenging componentmay be any one of a wide variety of transition metal chelates orcomplexes of polycarboxylic acids. Amino polycarboxylates, such as EDTA,and other polycarboxylates, optionally containing hydroxyl moieties, aswell as their salts or other derivatives, are representative examples ofpreferred compounds which can be complexed with lower oxidation statesof transition metal ions and used in this invention. Transition metalchelates of hydroxyethylene diamine triacetic acid, diethylene tridminepentacetic acid, or trans-1,2-diamino cyclohexane tetracetic acid canalso be used as suitable oxygen-scavenging compounds. Other transitionmetal chelates containing one or more amine, hydroxyl, carboxylate orsulfhydryl groups, or combinations thereof, may also be used.

These chelates are effective oxygen scavengers because the transitionmetal ion of the chelate becomes oxidized when the chelate contactsoxygen. It is well known that elements such as the transition metals canexist in any one of a number of oxidation states. Thus, the use of loweroxidation of transition metal ions is necessary for an appropriatedegree of oxygen scavenging. This lower oxidation state can be achievedin two ways: one is to utilize chelates state transition metals in theirlowest oxidation state (e.g., ferrous, cuprous, etc). Alternatively,when the transition metals are present in the chelate in their higheroxidation states (e.g., ferric, cupric, etc.), a reducing agent can beused to covert the metal ion to a lower oxidation state thus impartingoxygen scavenging properties to the chelate. As noted above, thepreferred reducing agents are the ascorbates.

In a further embodiment of the invention, a transition metal (preferablyiron) chelate of a particular salicylate salt, in particularFe⁺⁺⁺/Sal₃/3Na⁺3NaCl where Sal

can be used as the oxygen-scavenging material. Instead of this material,a wide variety of other salicylates can be used, including

were M is a transition metal, Y is an alkali metal such as Na, K, Ca orH, and R₁ and R₂ are carbon atoms or part of a benzene ring, or

where M is a transition metal, X is (CH₂)_(m) Z(CH₂)_(m) with m being aninteger, Z is N or C═C with the proviso that if Z is N then N is alsobonded to M, and R₁ and R₂ are carbon atoms or part of a benzene ring.

These salicylates are effective as oxygen scavengers because they reactwith oxygen to become oxidized. In addition, selection of a transitionmetal in its lower oxidation state enhances the oxygen scavengingperformance of these chelates. As noted above, if transition metals intheir higher oxidation state are utilized in these chelates, the oxygenscavenging properties of the chelate can be further enhanced by theincorporation of a reducing agent into the composition. Again, theascorbates are preferred reducing agents for the reasons given above.

A wide variety of carriers (or mixtures thereof) may be used inaccordance with the teachings of the present invention. For use inapplications such as crown or closure liners, the carrier is preferablya polymeric thermoplastic, such as PVC, EVA, PET, PE or PP, orpolyurethane. As noted above, PVC liners are well known for use incrowns. There is also well-known technology for making aluminum orplastic closures containing-EVA liners. Thus, one of the preferred usesof the compositions of the invention is a liner or gasket in a crown orclosure for capping a beverage bottle. Entire closures may also be madeof plastics containing the compositions of the invention (e.g.,all-plastic screw-on threaded caps for soft-drink bottles, and thelike).

In addition to its use as a crown or closure liner, the compositions ofthe invention may also be used in the form of a film for packagingmaterials. Such films are preferably made of PE, PP, PVC, or SURYLY™, aDuPont Corporation polymer. The oxygen scavenging compositions of theinvention could also be used for forming containers; in this situationthe polymer is preferably PET, PVC, or PE. Other polymers which arecontemplated by the invention include silicones as well as elastomerssuch as isoprene rubber and its rubber-like analogs: nitrile rubber,chloroprene, EPDM, etc. Silicone rubber can also be used in somesituations. The only requirements of the polymer are that it can beprocessed in a manner which allows the oxygen-scavenging composition tobe dispersed relatively uniformly throughout and that the polymer bepermeable to oxygen and water or water vapor.

Another application of the compositions of the invention would be as asachet, packet or pellet which is mounted on a support and then attachedto a crown or other container lid or to the container itself in the formof an article, such as a ring or spot, or as a coating. Thus, thecompositions can be applied to a wide variety of jar lids and caps whichare used for retaining food substances therein. Again, however, onepreferred use of the compositions of the invention is in connection withfoodstuffs which contain water so that the oxygen-absorbing compoundsmay be activated by contact with water or water vapor which permeatesinto the polymer. The compositions may also be used with dry products bypre-activating the composition via exposure to water or water vaporshortly before sealing the container.

Other uses for the compositions of the invention will be readilyapparent to those of skill in the art. By way of example, the usesinclude metal (i.e., aluminum or tinplate) cans for beverages. It isalso contemplated to prepare plastic bottles or other styles ofcontainers (e.g., tubs, cans, etc.) from or incorporating thecompositions of the invention. Another preferred use of the compositionof the invention is as a gasket or liner applied to an aluminum orplastic closure or metal crown for plastic or glass bottles. The oxygenscavenging composition of the invention may also be incorporated intothe materials used as an adhesive between adjacent layers of plastic orincorporated into the adhesive which holds adjacent layers together.

Other embodiments of the present invention are readily apparent to thoseskilled in the packaging arts, all of which embodiments fall within thescope of the invention and are intended to be included therein. Forinstance:

1) Many packages are constructed of transparent plastic films so thatthe product may be seen by the purchaser. Such packages usually haveprinted decoration incorporated therein, often actually printed on acentral layer of a multi-layer film so as to avoid the possibilities ofboth ink-contamination of package contents and rubbing off of theprinting during handling. An oxygen-scavenging composition of thepresent invention might be unobtrusively incorporated into such apackage by being printed onto the central layer underneath thedecorative or informative printing.

2) For other packages which do not comprise a separate closure (e.g.,sterile or refrigerated “brick-packs” such as often used for fruitjuices and the like; gable-top packages such as milk cartons; containersmade to have the contents expressed therefrom and not be resealed, suchas individual portions of condiments; or various film or foil bags madeto be torn open and not resealed, such as potato chip bags) acomposition of the present invention may be incorporated into thesealant or gasketing material used to hold the package closed. Forexample, oxygen-scavenging compositions of this invention can be printedonto the head space region of the package. Alternatively, thecompositions can form a laminated insert in the package.

3) Likewise, the composition of this invention might be applied as apaint or coating attached to the interior of the container, or as a tapeor similar item protruding into or exposed to the interior of thepackage and mechanically held in place by the closing mechanism ortechnique.

4) There may be instances in which the oxygen scavenger compositions ofthe present invention must be separated from the product: in such casesthe compositions may again be incorporated into an interior layer of amultilayer container.

5) The compositions of this invention may conveniently be combined withsolutions to other manufacturing problems. For example, a common problemin plastics manufacturing today is to safely recycle previously-usedplastic plastics into food-safe containers. Much recycled plastic mayhave been used as containers for random unknown materials, and therecycled plastics may therefore contain traces of materials notacceptable for food contact, and may also be composed of an admixture ofplastics highly and minimally pervious to oxygen. Use of such recycledmaterials, combined with the compositions of this invention, as an innerlayer in multiple-layer container construction would allow much easieruse of mixed-recycle materials.

In the plastics manufacturing art, “master batches” or concentrates ofvarious sorts are sometimes used in the preparation of final mixtures ofmaterials for eventual use in manufacturing finished articles. In thepresent invention, preparation and use of highly concentrated forms ofoxygen control chemicals in carrier (e.g., PVC, plastisol, epoxy cancoatings, gasketing, spray, roll-on, and dip coatings, and the like) isconvenient in the manufacture of the composition which will eventuallybe used as final oxygen-scavenging compositions of this invention. Thepresent invention lends itself readily to such practices, which arefully within the scope contemplated for the invention.

The resin concentrate form of this invention is particularly useful forshipping and storing oxygen scavenging compositions. It is much easierto handle than the uncombined oxygen scavenger and catalyst powders, andit is lighter and therefore more convenient to ship and store than thefinal diluted compositions. Further, it is easier to protectconcentrates against humidity conditions which could prematurelyinactivate component ingredients. For example, the concentrate can beshipped in sealed 55 pound bags. When the final fitment, film, or otherform of the composition is to be produced, the concentrate is dilutedwith a base resin to obtain an oxygen scavenging composition having theconcentration and form required for the end product. For example, theend user can combine the concentrate with a base resin in appropriateprocessing machinery.

In preferred embodiments, the concentrate is diluted in a ratio ofbetween about 1:38 and 1:1, and more preferably between about 1:13 and1:1 concentrate to base resin. In these concentrate formulations, it ispreferred to use an amount of oxygen scavenging compound ranging fromabout 10 to 50% by weight and more preferably from about 20 to 40% byweight (i.e., between about 500 and 2500, and preferably between 1000and 2000 micromoles of scavenger compound per gram of polymer forcompounds having molecular weights of between 200 and 500 grams permole). When an ascorbate is used as the scavenger, the catalyzing agentof the transition metal element compound or complex may be used in anamount of about 0.3 to 8% by weight (i.e., between 40 and 200 micromolesper gram of polymer). More preferably, the catalyzing agent is used inan amount of about 0.6 to 2% by weight.

In some preferred embodiments, two separate concentrates are employed,one containing the oxygen scavenging compound and the other containingthe catalyst. The oxygen scavenging compound is preferably present at aconcentration ranging from about 10 to 50% by weight and more preferablyfrom about 20 to 40% by weight in the first concentrate. The catalyzingagent is preferably present at a concentration ranging from about 0.3 to8% by weight and more preferably from about 0.6 to 2% by weight in thesecond concentrate. The carrier resin in the two concentrates may bedifferent but they should be compatible with each other in the finaloxygen scavenging composition. The two concentrates are combined in aratio that depends upon the particular application. By providingseparate concentrates, a master batch is provided that is not oxygenreactive and can be diluted to a lower concentration at the time a film,part, or fitment is made. This allows the master batches to be waterquenched without loss of activity during a processing step such as twinscrew compound extrusion. It also allows flexible control of the ratioof oxygen scavenger to catalytic agent. Generally, the ingredients forthe concentrates are well mixed, using low sheer and good temperaturecontrol. In subsequent processing, storage or transport, the concentrateshould not be exposed to moisture. In some cases, drying of the masterbatch prior to extrusion as well as storage of the resulting pellets inhigh moisture barrier bags is necessary.

When a PAPA chelate, macrocyclic chelate or amino polycarboxylic acid orsalicylic acid chelate of a transition metal ion is used as thecatalyzing agent in the compositions of this invention, these chelatesmay also be used to augment the oxygen scavenging properties of theascorbate compounds. To do so, such chelates should include a loweroxidation state transition metal ion and be used in an amount of betweenabout 0.3 and 33 and preferably, 2.5 to 15 parts per weight based on 100parts by weight of the polymer (i.e., between 10 and 500, and preferably50 to 300 micromoles per gram of polymer). Preferred transition metalchelates include polyalkyl polyamines or macrocyclic amine chelates oftransition metal ions such as iron, copper, nickel or cobalt. In thesepolyalkyl polyamine chelates, equal length carbon chains are utilizedbetween adjacent nitrogen atoms, preferably those chains having between1 and 4, and optimally 2, carbon atoms.

In other embodiments of the invention, these chelates may be utilizedalone as the sole oxygen scavenging compositions. In this embodiment,the preferred chelates mentioned above would be used in the same amountas described above for the ascorbates, rather than the amounts used forthe chelates as catalysts. If desired, the ascorbate compounds can beincluded as a reducing agent and would be used in the same amountdescribed above for the ascorbate catalysts. The ascorbates also act asa preservative for the chelate. When the ascorbates are included toaugment the oxygen scavenging of the chelates, then the amount usedwould be the same as described above for the chelates which are used toaugment the oxygen scavenging properties of the ascorbates.

Other transition metal chelates containing one or more amine, hydroxyl,carboxylate or sulfhydryl groups, or combinations thereof, may also beused to augment the oxygen absorbing properties of the composition.Transition metal chelates of salicylates or salicylate salts; aminopolycarboxylates, such as EDTA; and other polycarboxylates, optionallycontaining hydroxyl moieties, are representative examples of suitablecompounds. Hydroxyethylene diamine triacetic acid, diethylene triaminepentaacatic acid, or trans-1,2-diamino cyclohexane tetraacetic acid canbe used. As noted above, however, the transition metal ion should be ina lower oxidation state. Thus, monoferrous disodium EDTA[Fe⁺⁺/EDTA/2Na⁺] would be preferred, while monoferric monosodium EDTA[Fe⁺⁺⁺/EDTA/Na⁺] would be used in combination with a reducing agent,such as sodium ascorbate.

In other embodiments of the invention, these chelates may be utilizedalone as the sole oxygen scavenging compositions. In this embodiment,the preferred chelates mentioned above would be used in the same amountas described above for the ascorbates, rather than the amounts used forthe chelates as catalysts. If desired, the ascorbate compounds can beincluded as a reducing agent and would be used in the same amountdescribed above for the ascorbate catalysts. The ascorbates also act asa preservative for the chelate. When the ascorbates are included toaugment the oxygen scavenging of the chelates, then the amount usedwould be the same as described above for the chelates which are used toaugment the oxygen scavenging properties of the ascorbates.

In another embodiment of the invention, the oxygen scavengingcompositions may be treated to maintain these agents in a dry statebefore they are dispersed relatively uniformly throughout the polymer.Numerous methods are known for maintaining this dry state, and freezedrying, spray drying, or microencapsulation are preferred due tosimplicity of processing. Thereafter, the oxygen scavenging compositionwill be activated by contact with water or water vapor which permeatesinto the polymer. Techniques for freeze drying and microencapsulationare well known in the art, and one skilled in the art can select theappropriate encapsulant for the intended application. By suchappropriate selection of the encapsulating material, one may protect theenclosed oxygen scavenging compound from the oxygen in air; this wouldallow longer storage of the prepared oxygen scavenger. After freezedrying, spray drying, or microencapsulation, the materials are thenblended with the appropriate carrier and manufactured into the finalcomposition, form and configuration for use in, on or as the productpackaging.

By way of example, one way of distributing the oxygen scavengingmaterial throughout a carrier is by preparing direct blend polymers,either as “master batch” concentrates or as final product. As notedabove, such concentrates are often preferred because they contain lessinert material and are therefore less expensive to manufacture, storeand ship. For preparation of a concentrate or “master batch” which willbe diluted during manufacture of the final compositions, very highweight percentages of oxygen scavenging ingredients (up to, e.g.,greater than 40% and even up to 50%) may be used. Beads of a polymercarrier, such as polyvinyl chloride, low density polyethylene, orethylene vinyl acetate, are placed between the rollers of a polymerforming mill operating at about 300° F. The back roller of the milloperates at a higher velocity than the front roller. The rollers spin inopposite directions, so that the beads are sheared downwardtherebetween. As the polymer beads become fluid they spread across thefront roller at the thickness set between the rollers.

After the PVC has become heated and softened, the oxygen scavengingcompounds to be blended into the polymer are slowly poured into thespace between the rollers. The mixing of PVC, LDPE, or EVA and compoundis then achieved by cutting the polymer to the center of the mill andthen allowing it to spread back out over the roller. This is done 20-30times until the compounds are well mixed. The mixing may also be done inthe standard ways of commercial preparation of various plasticformulations, e.g., by simple addition of oxygen absorbing materials ofthe invention as an additional ingredient during bulk “dry mixing” ofPVC, plasticizer, and other components. In some preferred embodiments, aBanbury style batch mixer or a twin screw continuous mixer of the typecommonly used in the resin industry is used to combine the base resinwith oxygen scavenging ingredients.

EXAMPLES

The following examples illustrate preferred embodiments of theinvention. In each example, the formulation components are designated inparts by weight unless otherwise indicated.

Example 1

Crown liners were prepared from PVC resin containing the oxygenscavenging and catalyzing agents shown in Table I. These liners wereplaced in bottle crowns which were then used to cap fresh bottled beer.Oxygen measurements were made in six replicate samples immediately aftersealing and pasteurizing the bottles, and again after seven days ofstorage at room temperature. These oxygen measurements were made using apolarographic oxygen probe device from Orbisphere, Inc. Results areshown below in Table I.

TABLE I Samples (μ moles) Component Initial Control F G H I SodiumAscorbate — — 50 112.5 250 250 FeCl₂ — — 5 5 5 — CuSO₄ — — — — — 5Oxygen Content* (ppb) 415.4 229.1 135.1 106.6 83.2 121.4 *The controland samples F-I were measured after seven days.

These data show that beer, itself, consumes oxygen, which is one causefor the normal limited shelf life of this product. The use of a crownliner made of one of the polymer compositions of the invention resultsin removal of oxygen over and above that which is normally consumed bythe beer. Moreover, the greater the amount of ascorbate used for aparticular catalyst, the greater the amount of oxygen that is removed.

Example 2

An Erlenmeyer flask containing a magnetic stir bar is filled withdeionized water and corked. The water in the flask is stirred on amagnetic stir plate and flushed with a moderate flow of argon gas for ½hour until the dissolved oxygen in the water is displaced.

EDTA disodium salt dihydrate and ferrous chloride tetrahydrate, 1:1mole/mole, are placed in a second Erlenmeyer flask, which also containsa magnetic stir bar. The second flask is flushed with argon gas for tenminutes.

The deoxygenated water in the first flask is then introduced into thesecond flask (containing the EDTA and ferrous chloride) until thedesired amount of liquid has been transferred. The contents are keptunder argon, the solution is stirred on a magnetic stir plate, and thepH is adjusted to 5 with 10 M deoxygenated sodium hydroxide.

The solution is then transferred to an argon flushed lyophilizationflask and is frozen in liquid nitrogen. The frozen solution is thenlyophilized until all water has been removed. Oxygen-contaminatedsolutions are detectable by a color change from a light green to ared-orange color.

Example 3

A standard PVC lining compound was heated and mixed on a two roller millvia standard practice.

When the proper degree of fluidity was reached, the oxygen scavengingingredients were added and mixed into the compound. Sheets of compoundwere removed from the mill, cooled, and cut into pieces small enough tofit into a gas measurement cell. Results are as follows:

CELL LOADING, ONE GRAM COMPOUND OXYGEN (MOLES FERROUS EDTA/ SCAVENGEDμMOLES SODIUM ASCORBATE) (μMOLE/DAY) 0/0 1.2  0/101 1.8  0/252 4.0 0/353 4.3 46/0  7.0 131/0  14.4 209/0  17.4  21/127 10.3  21/208 14.142/85 12.1  42/163 16.8  41/245 22.2  2/124 14.8  62/208 20.0 83/83 16.5 82/163 21.2  80/240 26.0 123/123 24.8 156/156 30.4

The data shows that a standard PVC lining compound will react to a smallextent with oxygen. The addition of only sodium ascorbate (i.e., withouta source of transition metal catalyst) very slightly increases thereactivity. Ferrous EDTA has a significant effect on the amount ofoxygen scavenged. The combination of ferrous EDTA and sodium ascorbate,however, causes a disproportionate increase in oxygen scavenged. Bothferrous EDTA by itself and in conjunction with sodium ascorbatedemonstrate significant oxygen removal.

Example 4

Other compounds may advantageously be used in practicing this invention.For example, salicylic acid is a strong chelator for Fe⁺⁺⁺ (and less sofor Fe⁺⁺): the iron of the “chelated Fe⁺⁺” form will rapidly oxidize inthe presence of oxygen, analogously to the behavior of Fe⁺⁺ EDTA used inexperiments previously described herein. Consequently, an iron complexof salicylic acid (or a salt thereof) is also useful in practicing thepresent invention. The Fe⁺⁺⁺ (salicylic acid)₃ complex is less solublein aqueous solution than is the comparable Fe⁺⁺ EDTA complex;consequently such salicylic acid complexes should yield lower rates ofleach from container or gasket materials (wherein they are incorporated)into the contained products. Use of these oxygen-scavenging materialswould be preferred when the consideration is to minimize the leaching ofpackage components.

Furthermore, it is preferable to utilize the Fe⁺⁺⁺ (salicylic acid)₃complex in combination with an ascorbate as detailed above, so that thetransition metal ions from the complex can serve to catalyze the aerobicoxidation of the ascorbate, and/or the ascorbate can reduce theoxidation state of the ferric ion.

The following experiment illustrates the utility of this combination.

120 micromole/gram finished plastic of Fe⁺⁺⁺ (salicylic acid)₃ and 200micromole/gram finished plastic of sodium ascorbate were blendedtogether into PVC crown lining materials in accordance with techniquesknown in the art and as described above.

The resulting plastic material was used to form completed, lined crownsusing standard crown making machinery. To test for oxygen uptakecapacity, completed liners were then removed from crown shells, wettedwith 8% ethanol beer simulant, and placed in glass test chambers filledwith air. Oxygen absorption was measured versus time as change inpercent oxygen in the air in test chambers for replicate liners. Thesamples were analyzed using a gas chromatograph with a mass selective asis well known in the art. The results are as follows:

micromoles O₂ Absorbed 6 micromoles O₂ Absorbed (normalized to “per gram(normalized to “per gram Sample of liner”) at Hour 3 of liner”) at Hour27 R 14.0 28.6 S 10.5 26.7 T 10.5 26.1

To attain the desired combination of characteristics (e.g., low leachrate plus high oxygen absorption potential), certain modifications tosimple salicylate salts/complexes suggest themselves. For instance,leach rates might be appreciably lowered by chemically modifying thesalicylic complex to be more hydrophobic, hence, less soluble in aqueousmedia. Certain of these modifications are included in the formulae forsuitable salicylic acid derivatives described above.

Example 5

A concentrated low-density polyethylene (LDPE) oxygen scavenging polymer(“master blend”) containing 41 weight percent sodium ascorbate and 0.6weight percent copper sulfate (anhydrous) was prepared as follows. LDPEbase resin (Quantum Chemical Corporation, Cincinnati, Ohio) was mixedwith the oxygen scavenging ingredients in a Banbury style mixer. Theresulting mixture was converted into sheets on a two-roll mill whichwere then chopped into pellets and extruded into thin films.

To measure oxygen uptake, the thin films were punched into {fraction(15/16)}″ diameter disks and accurately weighed. The disks, one each,were placed in glass bottles containing 370 mL of air saturated waterand no headspace gas and closed with a crown closure. Twice each day,the bottles were agitated to mix the water in the bottle, eliminatingoxygen concentration gradients in the bottle. Dissolved oxygenconcentration was measured using a polarographic oxygen sensor and theoxygen uptake was calculated by calculating the difference in oxygenconcentration between bottles containing the disks and bottlescontaining no polymer. In general, five containers were measured at eachtime point.

The oxygen uptake from 2000 μmole/g ascorbate scavenger and 40 μmole/gcatalyst (normalized using a 0.3 g disk) was 310±70 μmoles O₂/g polymerafter 24 hours. At that time, all the available oxygen had been consumedfrom the container (91 μmoles of O₂ available in the bottle).

Oxygen uptake from 1000 μmole/g ascorbate scavenger and 20 μmoles/gcatalyst was observed as follows:

Oxygen uptake Time (μmoles/g polymer) 24 Hours 21 ± 4  48 Hours 30 ± 1172 Hours 40 ± 5 

The total oxygen capacity of the oxygen scavenging polymer was alsodetermined. In this case, samples of the above polymers (at 1000 and2000 μmole/g ascorbate loading) were frozen in liquid nitrogen andground in a small grinding mill until all the particles were smallerthan 15 mesh. The sample was then dried in a beaker for 1 hour at 50° C.A sample theoretically capable of scavenging 900 μmoles of oxygen (½ theoxygen in the container) was added to a 215 mL container containing 6 mLof water. The container was closed with a crown closure and stored at50° C. and measured 10, 14 and 21 days after bottling.

The total oxygen capacity from 2000 μmole/g ascorbate scavenger and 40μmole/g catalyst was 2540 μmoles/gram polymer, 127% of the theoreticalcapacity.

The oxygen uptake from 1000 μmole/g ascorbate scavenger and 20 μmoles/gcatalyst was 1350 μmoles/gram polymer, 135% of the theoretical capacity.

Example 6

The master blend from Example 5 was used to make thin films 0.001 to0.050 inches in compositions containing ratios of concentrate to baseresin of 1:0, 1:1, 1:3, and 1:7. The dilution was accomplished byshaking the desired ratio of master batch and base resin in a clearplastic bag and then dumping the contents into the desired processingequipment. In all the processes, the resin mixture containing materbatch was heated to a molten state and mixed before extruding, blowingfilm or injection molding. The resulting films were used in ketchupclosures, cosmetic closures and fragrance closures. In each case, theappropriate loading of oxygen scavenging material, in the form of tape,was glued to the inside of the gasket of a closure. In the case ofketchup, the headspace oxygen content monitored during the first 6 weekswas as follows. The container was a PET bottle with an oxygentransmission rate of 0.04-0.05 cc/package/day.

Control Closure O₂ Scavenger Closure Initial 20.3% 20.3% 24 Hour 18.9%17.8% 48 Hour 18.3% 16.8%  6 Day 14.0%  9.9% 16 Day 10.7%  5.2% 29 Day 8.5%  2.8% 56 Day  3.9%  1.1%

Headspace oxygen content was measured using an Ingold Instrumentspolarographic oxygen sensor model IL 307 with a soft package samplingdevice. To measure the bottle, a septum was applied to the outside ofthe inner seal of the closure and the inner seal was pierced by thesampling device. The gas inside the bottle was then analyzed for oxygencontent by the Ingold analyzer.

Color evaluations were taken after 4 months using a Hunter ColorAnalyzer. After four months, projected ketchup shelf life in the oxygenscavenger closure package was judged to be 20 months, and the controlwas judged to be 14 months.

The concentrate was also diluted in ratios of 1:13, 1:19, and 1:39 withbase resin to form injection molded fitments. The fitments were madewith Dowlex 2553 (Dow Chemical Co., Midland, Mich.) as the base resin.These fitments were tested on ketchup in a barrier bag. The barrier bagwas a multi-layer polymer bag with an oxygen transmission rate of 0.05cc/100²in/day. The fitments were heat sealed into the inside of the bagbefore the bag was made. One set of samples was held at 90 degreesFahrenheit and the another set was held at 100 degrees Fahrenheit. After75 days, color evaluations were made using the Hunter Color Analyzer. Nocontrol was run but the bag with the best color retention was the bagcontaining the 1:13 letdown of the oxygen scavenging concentrate. Thedifference in effectiveness between the fitments was most pronouncednear the top of the bag. In the body of the bag, away from the fitments,the effect was much less pronounced.

Example 7

The method described in Example 5 was used to prepare a concentrate ofethylene vinyl acetate (ELVAX 450, DuPont Company, Wilmington, Del.)having a 19.8 weight percent sodium ascorbate loading and a 0.3 weightpercent copper sulfate loading.

The film was made by extruding the EVA compound from a Brabenderextruder with a 1 inch wide ribbon die. The tape samples were evaluatedfor oxygen capacity using the method outlined in Example 5. The oxygenuptake from 1000 μmole/g ascorbate scavenger and 20 μmoles/g catalystwas as follows:

Oxygen uptake Time (μmoles/g polymer) 24 Hours 59 ± 8 48 Hours 79 ± 9 72Hours 110 ± 10

The total oxygen uptake from 1000 μmole/g ascorbate scavenger and 20μmoles/g catalyst was 1380 μmoles/gram polymer, 138% of the theoreticalcapacity.

Example 8

The master batch LDPE concentrate of Example 5 was combined with LDPEresin in a ratio of 1:1 and 1:7 and made into the following multilayerfilms: (A) a 3-layer film containing LDPE: Master Batch/LDPE (1:1):LDPE; and (B) a five layer film containing LDPE: Master Batch Tie-layerResin (7:1): EVOH: Master Batch/Tie-Layer Resin (7:1): LDPE. Themultilayer films were prepared using three one inch Killion Extruderswith a coat hanger design Killion combining adapter. The extruder wasconfigured in an ABCBA design, capable of extruding 3 different polymersin 5 layers. In each case, the die gaps were adjusted so that each layerwas of equal thickness. Film thickness for the 3 layer films ranged from0.005″ to 0.010″ and for the 5-layer films they ranged from 0.003″ to0.005″.

Oxygen transmission rates of the films were measured using a Moconoxtran 100 with a Mocon DL200 oxygen Rate Data Logger. To measure oxygentransmission rates, moist nitrogen was passed on both sides of a samplefilm until no oxygen was detected. Then moist air was blown across oneside of the film and the quantity of oxygen migrating through the filmwas measured. The oxygen transmission rate of the 3-layer LDPE filmsdecreased between 2 to 13 times less than the controls, depending uponpretreatment processes. The Mocon results are shown in the followingtable:

Oxygen Transmission Rates for 3-layer LDPE Film Samples OxygenTransmission Thickness Rate Sample (Mils) Pretreatment (cc/m²/da)control 5.1 none 2270 control 5.2 boiled 1 h, N₂ 3160 LDPE/MB (1:1) 5.0none 1160 LDPE/MB (1:1) 5.4 boiled 5 min, N₂  500 LDPE/MB (1:1) 5.6boiled 1 h, N₂  240 LDPE/MB (1:1) 5.5 55° C., 21 h, N₂  190

Oxygen transmission rates of the 5-layer films showed that the oxygentransmission rate of the film did not change when exposed to extremeheat and humidity. In contrast, the oxygen transmission rate through atypical 5-layer EVOH laminate increases 10 to 100 times during exposureto extreme head and humidity as experienced during typical retort cycles(40 minutes @ 250° F. and 100% RH).

What is claimed is:
 1. An oxygen scavenging concentrate comprising apolymeric carrier which is permeable to oxygen and water or water vapor;a D- or L-ascorbic acid or a salt thereof which is dispersed relativelyuniformly throughout the polymeric carrier in an amount ranging fromabout 10 to 50% by weight of the concentrate, the ascorbic acid or saltthereof being reactive with oxygen after activation with water or watervapor which permeates the polymeric carrier; and a catalyzing agent inan amount effective to increase the rate of reaction of the ascorbicacid or salt thereof with oxygen which is present in or permeatesthrough or into the polymeric carrier.
 2. The concentrate of claim 1wherein the salt of said ascorbic acid is a sodium, potassium or calciumsalt of D- or L-ascorbic acid.
 3. The concentrate of claim 1 whereincatalyzing agent includes iron, copper, nickel or cobalt.
 4. Thecomposition of claim 1 wherein the catalyzing agent is a transitionmetal compound, complex or chelate.
 5. The concentrate of claim 4wherein the transition metal compound is supplied as a sulfate orchloride salt.
 6. The concentrate of claim 5 wherein the transitionmetal compound is iron sulfate, iron chloride or copper sulfate, and isused in an amount of about 0.3 and 8% by weight of the concentrate. 7.The concentrate of claim 1 wherein the ascorbic acid is sodium ascorbateand the catalyzing agent is copper sulfate.
 8. The concentrate of claim1 wherein the carrier is a polymer selected from the group consisting ofpolyethylene, ethylene vinyl acetate polymer, polyvinyl chloride,ethylene vinyl alcohol, ethylene/alpha-olefin copolymers, andethyl-octene copolymers.
 9. A two-part oxygen scavenging systemcomprising: a first concentrate including, a first polymeric carrierwhich is substantially free of catalyzing agents and is permeable tooxygen and water or water vapor, and D- or L-ascorbic acid or a saltthereof dispersed throughout the first carrier in a concentration ofbetween about 10 and 50% by weight and being reactive with oxygen afteractivation with water or water vapor; and a second concentrateincluding, a second polymeric carrier which is substantially free of theD- or L-ascorbic acid or a salt thereof; and a catalyzing agentdispersed throughout the second carrier in a concentration of betweenabout 0.3 and 8% by weight, the catalyzing agent when combined with theD- or L-ascorbic acid or a salt thereof in a predetermined amountincreases the rate of reaction of the D- or L-ascorbic acid or saltthereof with oxygen.
 10. The system of claim 9 wherein the first andsecond carriers are the same.
 11. The two-part oxygen scavenging systemof claim 9 wherein the D- or L-ascorbic acid or a salt thereof is sodiumascorbate.
 12. The two-part oxygen scavenging system of claim 9, whereinthe catalyzing agent is copper sulfate.
 13. The two-part oxygenscavenging system of claim 9 wherein the first and second polymericcarriers are selected from the group consisting of polyethylene,ethylene vinyl acetate, polyvinyl chloride, ethylene vinyl alcohol,ethylene/alpha-olefin copolymers, and ethyl-octane copolymers.
 14. Theconcentrate of claim 1 wherein said catalyzing agent is selected fromthe group consisting of iron chloride and copper sulfate.